Switchover or reversing valves are widely used in the control of hydraulic systems and may be responsive to the arrival of a working piston at the end of a working stroke to reverse the fluid flow to the working cylinder and thereby allow the working piston to be displaced into an opposite position.
Such switchover or reversing valves have appropriate ports which can be connected to a source of hydraulic fluid, to a drain or reservoir for the return of the hydraulic fluid and to opposite sides of the working cylinder, for example, and may have valve seats between these ports which are engaged by a hollow valve piston to control the flow of the hydraulic fluid.
The valve piston may, in turn, be displaceable in a valve housing and generally has two extreme positions representing the two states of the valve and the two directions of flow which the valve is capable of generating in the hydraulic system as a whole.
Such valves and the related working piston may be used, for example, in hydraulically controlled apparatus of various kinds. For example, the valve may be used to control a hydraulically actuated log splitter, hydraulic press, compactor or pusher-type conveyor.
In general, these valves have the advantage that upon the development of large hydraulic restoring forces, the hydraulic valve piston may not effectively be shifted in the opposite direction or at least reliably shifted in an opposite direction. As a consequence, the displacement of the valve member from one seat in the direction of another seat may not reliably occur and hence, at least in some cases, the switchover between positions of the valve cannot be ensured.